As mentioned above, Southern in Mildura operated 2 Titans on RPT, (additional to the Air Ambulance Titans) VH-DLF/UOP mainly on the MQL-RMK-ADL and MQL-BHQ runs. They did provide some 'back-up' to the Shorts and then the Dash-8 to MEL from time to time until they were sold around 96 or 97. They were painted in TN colours then full QF colours when QF took over TN.
I don't recall any other piston types operating to MEL at that time.